Is there a forumla to know the cost for each Empty-Full EV charge?

Discussion in 'Prime Main Forum (2017-Current)' started by stevepea, Apr 25, 2017.

  1. bisco

    bisco cookie crumbler

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    how many watts are involved from the lowest possible hv starting point, and the highest?
     
  2. mr88cet

    mr88cet Senior Member

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    OK, that also makes more sense in terms of battery capacity. 5.5-6KWh (my impression from various sources) for HV operation, out of the 8.8KWh leaves 2.8-3.3KWh. If 1.2ish of it is reserved for HV operation (as I recall, that's more or less what a traditional Prius NiMH has) then there would leave 1.6-2.1KWh for charging overhead, which seems plausible.


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  3. giora

    giora Senior Member

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    With the PiP when the battery was new:
    It was measured by several that the EV portion is from 85% SOC to 23% SOC (i.e. 62% of 4400 Wh or 2730 Wh). The HV portion, from 6 to 2 bars (from optimum to minimum allowed) is from 23% SOC to about 17% SOC (i.e. 5% of 4400 Wh or 220Wh.
    If we assume that the prime has same buffers as the PiP we get:
    17% of 8800 lower buffer or 1500 Wh.
    220 Wh for HV (from minimum allowed to optimum HV SOC) same as PiP.
    15% of 8800 upper buffer or 1320 Wh.
    So this leaves about 8800-(1500+220+1320)=5760 Wh for the EV portion or about 5760+220=5980 Wh from minimum SOC allowed to 'full'.
    These are energies into the battery, divide by ~0.9 to get energy from the wall at 240V or ~0.85 in case of 120V.

    If you ask the amount from lowest possible HV to the highest still in HV I would estimate about 500 WH (similar to usable charge of the liftback).
     
    #23 giora, Apr 25, 2017
    Last edited: Apr 25, 2017
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  4. Lee Jay

    Lee Jay Senior Member

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    Switching power supplies hae two primary sources of loss - conduction loss and switching loss. Conduction loss is proportional to current squared and switching loss is usually proportional to voltage or voltage squared. Converter topologies vary a lot, but it's not uncommon for these two sources of loss to be approximately equal.

    If switching loss is proportional to battery voltage, then it's constant because that doesn't change. If it's proportional to input voltage then it's constant with energy because power transfer goes up as fast as switching loss does.

    In reality, it's always a mix because different portions of the converter have different sources of switching loss and different voltages across the switches.
     
  5. Lee Jay

    Lee Jay Senior Member

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    No, that 2kwh or so is reserved to preserve battery longevity by not allowing it to discharge to 0% and not allowing it to charge to 100%.
     
  6. mr88cet

    mr88cet Senior Member

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    Yes, "charging overhead."


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  7. Lee Jay

    Lee Jay Senior Member

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    That's a totally inaccurate description, in my opinion. Overhead implies losses associated with charging. It isn't that at all. It's intentionally unused capacity, and it's at both ends - charging and discharging.
     
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  8. bisco

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    so, 500 wh can change the 6.4 to anywhere from 5.9 to 6.9?
     
  9. giora

    giora Senior Member

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    No.
    6.3-6.4 kWh is probably from what I call 'optimum HV SOC' i.e. where the system prefers to be in (for the PiP - 6 bars), so the range may be 6.0 to 6.6 kWh from wall when starting with no EV miles and using L1.
     
    #29 giora, Apr 25, 2017
    Last edited: Apr 25, 2017
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  10. bisco

    bisco cookie crumbler

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    gotcha, thanks!
     
  11. bwilson4web

    bwilson4web i3 and Prime

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    Typical efficiency curves found in the switching regulator data sheets:
    [​IMG]

    From Digikey: https://www.digikey.com/en/articles/techzone/2011/dec/design-trade-offs-in-integrating-an-inductor-into-a-power-module
    article-2011_Fig2.jpg
    Bob Wilson
     
    #31 bwilson4web, Apr 25, 2017
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  12. Lee Jay

    Lee Jay Senior Member

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    I was trying to figure out what point you were trying to make, when I realized we were talking past each other.

    You're talking efficiency, I'm talking losses. Losses can go down and efficiency can go down at the same time.

    Also, those parts mentioned in that Digikey article are for tiny power supplies. Larger systems may operate with not only different parts, but different principles. In fact, some types of power supplies operate at nearly-constant efficiency over a huge range of power levels (laptop power supplies are like this). Special techniques are used to create this capability, such as highly-variable switching frequencies (very slow at very low power levels). Current-controlled switching mode can be used for this.
     
  13. Rmay635703

    Rmay635703 Senior Member

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    Remember folks much of the loss is to power cooling and monitoring systems which are fairly constant draws.

    So not all the lost power is charging loss
     
  14. Gen 3 for me

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    So losses are greater with lower charging voltages and lower current.

    And in Post #31 I believe Mr Wilson's graphs show that lower charging voltages have greater efficiency. Correct me if I'm wrong.

    I believe I have read that charging faster is worst for battery longetivity as compared to slow charging.
    I am not very concerned with the amount of EV miles I can get out of a charge. But will I promote longer traction battery life by using 120V - 8A charging as opposed to using any of the faster charging options? (I have plenty of time to charge on the 8A option overnight in my garage.)
     
  15. bwilson4web

    bwilson4web i3 and Prime

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    I'm having a senior moment but someone had posted a link to a Dept of Energy study of PiP charging efficiency. Hopefully they'll repost it as it showed higher efficiency at higher voltages and current ... and correct this my old man memory. Then I checked the switching regulator data sheets from Maxxim and one other and saw the pattern.

    UPDATE: Charging System Testing - Vehicle Charging System Testing | Advanced Vehicle Testing Activity

    I was remembering BMW i3 charging.

    We agree that (I**2)*R losses would increase with higher current but there is also a loss associated with the switching overhead that should be independent of the power output. I also can see the absolute losses increasing at higher power levels but the overhead for switching remaining the major, somewhat fixed regardless of power and voltage loads.

    Bob Wilson
     
    #35 bwilson4web, Apr 26, 2017
    Last edited: Apr 26, 2017
  16. GT4Prius

    GT4Prius Active Member

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    The answer that has been given about promoting battery longevity by using 8A, is, as I recall,

    1. This facility is provided by Toyota for those whose charging sources may be overloaded by a higher charge rate, not for protecting the car battery

    2. Battery longevity is dependent on many variables but the most significant is heat. Probability of significant loss of longevity due to charging at 16a is low, and this is also backed up by the fact that Toyota, cautious as they are, provide that capability for the car.

    I charge at 240v 16A. and I'm happy that this is safe enough for the battery.

    See the thread on battery life cycles.

    Changing the subject, my latest data so far concerning charging stats reported by my intelligent charger, for a full charge from zero charge level:

    1. 5.9 kwh
    2. 6.0 kwh
    3. 6.2 kwh*
    4. 6.1 kwh

    EDIT *Just remembered that this one included using the Heater on a cold morning for about 10 minutes powered by the charger using the Remote Climate facility.

    Posted via the PriusChat mobile app.
     
    #36 GT4Prius, Apr 26, 2017
    Last edited: Apr 26, 2017
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  17. Lee Jay

    Lee Jay Senior Member

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    Switching loss changes with voltage.

    Think (simplistically) of switching loss as shorting out the parasitic capacitances of the switching devices (including diodes). Energy = 1/2 * C * V^2, so the switching loss changes with the voltage the devices are blocking.

    Now, that voltage could be battery voltage, grid voltage (times sqrt(2)), or some combination, but it's definitely related to voltage. How is dependent on topology and modulation strategy.
     
  18. bwilson4web

    bwilson4web i3 and Prime

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    Not to worry, I put the Prius Prime on 12A, 120VAC charging this morning via a Kill-a-Watt. When I get home, I'll read out and share the metrics. Then we can compare it to the L2 charging @16A already shared.

    Bob Wilson
     
  19. JasonG

    JasonG Member

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    I was doing full charges at work using a chargepoint when it was free for the first 3 months... :) The most it ever recorded was 6.24 kWh. That was a 220V charger. This seems to be close to charging at home on 110v but difficult to tell as there is the background usage even over night.
     
  20. bwilson4web

    bwilson4web i3 and Prime

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    The Kill-A-Watt reports 6.31 kWhr.

    Bob Wilson
     
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